index fossils: evolution and biostratigraphy
DESCRIPTION
Index Fossils: Evolution and Biostratigraphy. Evolution. Variations exist within a population Result from mutations and other genetic accidents Some variations are advantageous Others are not Some are neutral Natural Selection works on these variations - PowerPoint PPT PresentationTRANSCRIPT
Index Fossils: Evolution and Biostratigraphy
Evolution
Variations exist within a population Result from mutations and other
genetic accidents Some variations are advantageous Others are not Some are neutral Natural Selection works on these
variations Characteristics of population shift
through time = evolution
What is Natural Selection?
What phrase is commonly used to describe Natural Selection?
“Survival of the fittest” What does it mean? Organisms best suited to the environment
survive long enough to reproduce. Advantageous traits are passed on
How do new species arise?
When accumulated variations are great enough that some individuals within the population cannot interbreed, a new species has arisen.
New species commonly arise in geographically or environmentally isolated areas.
New species and original species may exist at same time
Bio-Events
First appearances of new species First appearances of new higher taxa Extinctions of species Mass extinctions of multiple taxa Bio-events are unique points in geologic
time
Index Fossils
Some fossils are more useful than others for relative age determinations
Fossils that are most useful are called INDEX FOSSILS
What factors would maximize a fossil’s usefulness? (i.e., What makes a good index fossil?)
What makes a good index fossil?
Distinctive appearance/easy to recognize
Short duration between first appearance and extinction (a.k.a. RANGE)
Widespread geographic distribution (makes correlation possible across a wide area/multiple continents)
Characteristics of Index Fossils
Limited Stratigraphic Range Widespread Geographic Distribution Commonly Pelagic Or, tolerant of a wide variety of
environments (found in many facies)
Mile Markers in Deep Time
Life is unique for each interval of time because of evolution and extinction
Volcanos, earthquakes, mountains, types of rocks repeat throughout history
Life does not repeat – it is directional Therefore, we can place other Earth
events in a framework based on fossils
Mile Markers in Deep Time
The fossil-based framework for Earth history is known as the GEOLOGIC TIME SCALE
Units: Eras, Periods, Epochs, Ages
Boundaries between units are based on bio-events
Index Fossils andInternational Stratotypes
The Case of the Silurian – Devonian Boundary
Dr. Ivo Chlupáč and Karlstejn
Index Fossils and theSilurian - Devonian Boundary
Graptolites * Conodonts * Chitinozoans * Trilobites Brachiopods Cephalopods
Definition ofthe S-D Boundary
Stratotype: Klonk, near Suchomasty, Czech Republic
S-D GSSP
GSSP = Global Stratotype, Sequence and Point
First appearance of Monograptus uniformis uniformis
Bed 20 Klonk, Czechia
Preserving the Stratotype